Abstract Community violence exposure (CVE) among Black emerging adults ages 18-29 in the United States is a major public health concern given its prevalence49 and association with substance use49,52. However, the nature of the relationship between CVE and substance use when the perpetrator(s) of the violence has an entrusted professional role to serve, enhance, or safe guard the welfare of the citizens they serve (e.g., police officers, doctors, teachers, etc.) and the violence (e.g., homicide and other types of serious physical harm) is experienced as a racism-based traumatic event (sudden, out of one?s control, emotionally painful, prejudicial, and discriminatory) is unknown. Exposure to police use of force in America is one type of CVE that has attracted national attention1,33,43. Nationally, Black emerging adults are three to four times more likely to experience exposure to police threat or use of force and two to three times more likely to be unarmed and killed in comparison to their white counterparts21,61,62. Prior research suggests that this type of CVE may be experienced as a racism-based traumatic event7,9. The Classes of Racism Frequency of Racial Experiences (CRFRE) measure12 was developed to assess individuals? exposure to perceived racism-based events. However, the CRFRE hostile-racism scale does not capture exposure to perceived racism-based police use of force events or the range of police use of force events that are most salient for a population. In addition, the nature of the relationship between exposure to racism-based police use of force, racism-based trauma symptoms, and substance use is unknown. Therefore, the proposed study will 1) Identify key survey items to add to the CRFRE hostile-racism scale that capture exposure to racism-based police use of force among a sample of Black emerging adults receiving services from Fathers? Support Center or St. Louis County Justice Services in Saint Louis, Missouri, or enrolled in St. Louis Community College 2) Conduct a pilot study to test the psychometric properties of the revised CRFRE scale, and 3) Test the potential mediating effect of racism- based trauma symptoms on the relationship between exposure to racism-based police use of force and substance use. Findings from the study will advance our methodology for quantifying exposure to racism- based police use of force and elucidate specific pathways to substance use for Black emerging adults. Additionally, the applicant?s proposed training plan will allow him to: 1) advance his substantive and measurement knowledge regarding exposure to racism-based police use of force, racism-based trauma symptoms, and substance use; 2) enhance his knowledge and skills in psychometric analysis; and 3) increase his skills for effective dissemination of research findings. The proposed research and training plans will help prepare the applicant for a career as an independent racism-based trauma and substance use scholar focused on advancing knowledge of prevalence and population level disparities in exposure to racism-based traumatic events and informing culturally relevant substance use prevention programs for Black emerging adults.